Processless lithographic printing plate precursor

ABSTRACT

A radiation-sensitive medium comprises hydrophilic polymer particles, the particles comprising a thermally softenable hydrophobic polymer, a hydrophilic polymer and a bonding compound capable of chemically bonding to the hydrophobic polymer and to the hydrophilic polymer. The radiation-sensitive medium further may comprise a substance capable of converting radiation into heat. The radiation-sensitive medium is aqueous-ineluable when coated and dried, and becomes hydrophobic under the action of heat. The polymer particles are made by polymerization of at least one hydrophobic monomer and at least one bonding compound in the presence of the hydrophilic polymer. The radiation-sensitive medium may be provided as a coatable composition to be applied to substrates to form a processless radiation-imageable lithographic printing precursor, which may further be provided with an aqueous eluable hydrophilic overcoat. The processless radiation-imageable lithographic printing precursor so created may be imaged using absorbed radiation that is imagewise converted to heat, resulting in areas of hydrophobic property, while unimaged areas retain their hydrophilic property. This allows the latent image so formed to be employed in creating a negative-working lithographic printing master. The negative-working lithographic printing master so created is irreversible, does not require a substrate of controlled hydrophilicity and provides great toughness in the exposed areas. The radiation-sensitive medium may be coated on-platesetter or on-press onto a suitable substrate, including the drum of the press. It may also be coated off-press on a suitable substrate to create a precoated processless radiation-imageable lithographic printing precursor.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional application No.60/436,182 filed on Apr. 14, 2003, and is a continuation-in-part ofapplication Ser. No. 10/647,913, filed Aug. 25, 2003.

FIELD OF THE INVENTION

This invention relates to image formation in printing plates andprinting plate precursors and to the formation of images directly fromelectronically composed digital sources without wash-off development.

BACKGROUND OF THE INVENTION

For many years, it has been a goal of the printing industry to formprinting images directly from an electronically composed digitaldatabase, for example, by a so-called “computer-to-plate” system. Theadvantages of such a system over the traditional methods of makingprinting plates are the elimination of the costly intermediatesilver-containing film and processing chemicals; a saving of time; andthe ability to automate the system with consequent reduction in laborcosts.

The introduction of laser technology provided the first opportunity toform an image directly on a printing plate precursor by directing alaser beam at sequential areas of the printing plate precursor andmodulating the beam so as to vary its intensity. In this way, radiationsensitive plates comprising a high sensitivity photocrosslinkablepolymer coating have been exposed to imagewise distributions ofradiation from various laser sources and electrophotographic printingplate precursors having sensitivity ranging from the visible spectralregion into the near infra-red region (including thermal sensitivity)have been successfully exposed using low powered air-cooled argon-ionlasers and semiconductor laser devices.

While lithographic printing precursors that are post-exposuredevelopable using aqueous media, preferably alkaline aqueous media, arewell known and widely used in the printing industry, there is a morespecific subset of precursors that may be developed on press by theaction of the fountain solution employed during wet offset printing. Anewer class of lithographic media is based upon the general concept ofemploying polymeric particles in an otherwise hydrophilic binder, oftenalong with a substance to convert light into heat This kind of media isexemplified by U.S. Pat. No. 6,001,536. The unilluminated areas of alithographic precursor based on this generic media may be removed bytreatment with fountain solution on a printing press. This kind ofprecursor is therefore pseudo-processless, in that no specific separatedevelopment step with a specific developer, as such, is required toobtain a master. The illuminated areas are rendered hydrophobic andhence the master is in effect negative-working. These precursors allowlithographic printing masters to be made relatively easily on-press, butsuffer from poor run length. The quality of the printed image renderedis directly dependent on the choice and quality of hydrophilic substrateused, as this substrate is exposed and has to carry the fountainsolution during the wet offset printing process.

A more specific category of lithographic precursors employs mechanismsand compositions that cause the sensitive layer on the substrate toswitch between hydrophilic and hydrophobic, without any material beingrequired to be removed with a development step. That is, there is noremoval of material at all, even by fountain solution. These are trueprocessless precursors.

By way of example, U.S. Pat. No. 6,410,202 describes a composition forthermal imaging comprising a hydrophilic heat-sensitive polymer havingrecurring ionic groups within the polymer backbone or chemicallyattached thereto. The imaging members of this particular invention donot require post-imaging wet processing and are generallynegative-working in nature. In some cases, the polymers are crosslinkedupon exposure and provide increased durability to the imaging members.In other and preferred cases, the polymers are crosslinked uponapplication to a support and curing. A further example of this class ofprecursor is provided by U.S. Pat. No. 5,985,514. That patent describesan imaging member that is composed of a hydrophilic imaging layer havinga hydrophilic heat-sensitive polymer containing heat-activatablethiosulfate groups, and optionally a photothermal conversion material.Upon application of energy that generates heat, such as from IRirradiation, the polymer is crosslinked and rendered more hydrophobic.The exposed imaging member can be contacted with a lithographic printingink and a fountain solution and used for printing with or withoutpost-imaging wet processing. U.S. Pat. No. 4,081,572 describes makinghydrophilic printing masters comprising coating a self-supporting mastersubstrate with a specific hydrophilic polymer containing carboxylic acidfunctionality and selectively converting this polymer in imageconfiguration to a hydrophobic condition by heat. The polymer isselectively converted to a hydrophobic condition in image configurationthrough heat-induced cyclodehydration reactions. In other examples theprecursor is inherently positive-working, as in the case of U.S. Pat.No. 4,634,659. That particular patent describes a method of making aprocessing-free planographic printing plate comprising irradiating aplate surface comprised of a hydrophobic organic compound capable ofbeing converted, upon exposure to radiation, from hydrophobic tohydrophilic, carrying out the exposure in an image pattern, therebyselectively converting said surface, in the image pattern, fromhydrophobic to hydrophilic, thereby making the precursorpositive-working.

A yet more specific category of true processless lithographicprecursors, is based on media comprising polymer-based particles ormicrocapsules:

In U.S. Pat. No. 6,550,237 a heat-sensitive material is described formaking a negative working non-ablative lithographic printing plateincluding in a heat sensitive layer thermoplastic polymer beads and acompound capable of converting light into heat on a surface of ahydrophilic metal support. The layer is free of binder, and ischaracterized in that the thermoplastic polymer beads have a diameterbetween 0.2 μm and 1.4 μm. Argument is provided for the requirement thatthe thermoplastic particles should have a specific size range. It isexplained that, when the polymer particles are subjected to atemperature above the coagulation temperature they coagulate to form ahydrophobic agglomerate so that at these parts the metallic supportbecomes hydrophobic and oleophilic. Preferably, the polymer particlesare selected from the group consisting of polyvinyl chloride,polyvinylidene chloride, polyacrylonitrile, polyvinyl carbazole etc.,copolymers or mixtures thereof. Most preferably used are polystyrene,polyacrylate or copolymers thereof and polyesters or phenolic resins. Noindication is given that the polymer particles should be hydrophilic, orthat there may be more than one polymer in the particles.

In U.S. Pat. No. 6,653,042, a lithographic printing plate precursorrequiring no development step is described. It comprises a support,having provided thereon a layer comprising a hydrophilic medium, whereinthe layer comprising a hydrophilic medium contains a hydrophobitizationprecursor having a hydrophilic surface and a light-heat converting agentwhich is hydrophilic in itself, or at least on the surface. Variousimplementations of the invention are presented in which thehydrophobitization precursor having a hydrophilic surface is a particledispersion of composite constitution containing a hydrophobic substanceat the core part and having a surface layer of specifically superficialhydrophilicity. All forms of particles disclosed are composed of eitherone or two distinct materials. Various materials may be at the core,including hydrophobic polymeric materials and crosslinking materials. Alight-to-heat converting material, which is specifically chosen to behydrophilic, is also added. The lithographic printing plate precursor asdescribed above, further comprises a water-soluble protective layer.

U.S. Pat. Nos. 5,569,573 and 6,171,748 describe a thermosensitivelithographic printing original plate comprising a substrate, ahydrophilic layer containing a hydrophilic binder polymer, and amicrocapsuled oleophilic material which forms an image area by heating;the hydrophilic binder polymer having a three-dimensional cross-link anda functional group which chemically combines with the oleophilicmaterial in the microcapsule when the microcapsule is ruptured, and themicrocapsuled oleophilic material having a functional group whichchemically combines with the hydrophilic binder polymer when themicrocapsule is ruptured. Among the many hydrophilic binder polymerslisted are polysaccharides. The lithographic printing plate has ahydrophilic polymer thin film layer on the surface of the hydrophiliclayer. This hydrophilic thin film layer inhibits the surface fromaccepting tinting materials.

U.S. Pat. No. 6,513,433 (Inoue et al.) provides a lithographic printingplate precursor comprising a hydrophilic support having thereon aheat-sensitive layer containing a thermoplastic particulate polymerhaving Tg of not lower than 60° C., and at least one of a particulatepolymer having a heat-reactive group and a microcapsule containing acompound having a heat-reactive group incorporated therein. Thelithographic printing plate precursor of U.S. Pat. No. 6,513,433 furthercomprises a water-soluble overcoat layer provided on the heat-sensitivelayer. Inoue et al. theorize that when subjected to heat mode exposure,the lithographic printing plate precursor according to the inventionundergoes heat reaction of the microcapsules containing a particulatepolymer having a heat-reactive group or a compound having aheat-reactive group incorporated in the heat-sensitive layer to enhancethe strength on the image area and hence provide an excellent impressioncapacity. It is also thought that the thermoplastic particulate polymerwhich has once been melted becomes solidified when the temperaturereturns to ordinary value after exposure, whereby the strength can befurther enhanced on the image area which has been exposed in a heatmode, providing better impression capacity.

U.S. Pat. Nos. 5,677,108, 5,677,110 and 5,997,993 disclose an on-pressdevelopable lithographic printing plate precursor comprising alithographic hydrophilic printing plate substrate, a photohardenablephotoresist, and a layer of polymeric protective overcoat. The overcoatfunctions as an oxygen barrier, as well as imparting the plate with anon-tacky surface and an enhanced resistance to the adverse influence ofambient humidity. The overcoat contains a polyphosphate salt and mayfurther contain a fountain soluble or dispersible crystalline compoundto facilitate on-press removability. U.S. Pat. No. 6,387,595 disclosesan on-press developable lithographic plate comprising on a substrate aphotosensitive layer and a top ultra-thin ink and/or fountain solutionsoluble or dispersible overcoat with coverage of 0.001 to 0.150 g/m².

Heat-sensitive lithographic printing plates not requiring a wetdevelopment step after exposure have been desired by the industry for along time. One approach to no-process lithographic printing platesrelies on ablation to physically remove the imaging layer from theprinting plate precursor. Unfortunately, ablative printing plates canonly be exposed on imaging devices that are fitted with a vacuum deviceto collect the by-products of the ablative imaging step (particulate andgaseous debris). Recently the use of a laser transparent, water-solubletop coating over an ablatable imaging layer such that when ablativelyremoved with a laser, the ablative debris is contained by the topcoating, has been proposed. See for example WO99/41077, U.S. Pat. No.6,397,749, U.S. Pat. No. 6,468,717 and U.S. Pat. No. 6,468,717.

A water-soluble overcoat may also be provided to protect the hydrophiliclayer during storage and handling and to improve lithographic latitude.See for example U.S. Pat. No. 5,997,993, U.S. Pat. No. 6,171,748, U.S.Pat. No. 6,468,717, U.S. Pat. No. 6,503,684 and U.S. Pat. No. 6,513,433.

There remains a requirement for negative-working, true processless,lithographic precursors having long run-length, suitable sensitivity tolaser-diode-based imaging radiation, and which are easy to prepare,preferably from aqueous media, and show consistent high quality pressperformance and good handling characteristics.

SUMMARY OF THE INVENTION

A radiation-sensitive medium comprises hydrophilic polymer particles,the particles comprising a thermally softenable hydrophobic polymer, ahydrophilic polymer and a bonding compound capable of chemically bondingto the hydrophobic polymer and to the hydrophilic polymer.

The radiation-sensitive medium further may comprise a substance capableof converting radiation into heat. The radiation-sensitive medium isaqueous-ineluable when coated and dried, and becomes hydrophobic underthe action of heat. The polymer particles are made by polymerization ofat least one hydrophobic monomer and at least one bonding compound inthe presence of the hydrophilic polymer. The radiation-sensitive mediummay be provided as a coatable composition to be applied to substrates toform a processless radiation-imageable lithographic printing precursor,which may further be provided with an aqueous eluable hydrophilicovercoat. The processless radiation-imageable lithographic printingprecursor so created may be imaged using absorbed radiation that isimagewise converted to heat, resulting in areas of hydrophobic property,while unimaged areas retain their hydrophilic property. This allows thelatent image so formed to be employed in creating a negative-workinglithographic printing master. The negative-working lithographic printingmaster so created is irreversible, does not require a substrate ofcontrolled hydrophilicity and provides great toughness in the exposedareas. The radiation-sensitive medium may be coated on-platesetter oron-press onto a suitable substrate, including the drum of the press. Theradiation-sensitive medium of the present invention may be coatedoff-press on a suitable substrate to create a precoated processlessradiation-imageable lithographic printing precursor.

DETAILED DESCRIPTION OF THE INVENTION

In a first aspect of the invention there is provided aradiation-sensitive medium comprising hydrophilic polymer particles, theparticles comprising a thermally softenable hydrophobic polymer, ahydrophilic polymer and a bonding compound capable of chemically bondingto the hydrophobic polymer and to the hydrophilic polymer. Theradiation-sensitive medium further may comprise a substance capable ofconverting radiation into heat. The radiation-sensitive medium isaqueous-ineluable when coated and dried, and becomes hydrophobic underthe action of heat.

In a further aspect of the invention there is provided a method formaking the radiation-sensitive medium of the invention by polymerizationof at least one hydrophobic monomer and at least one bonding compound Inthe presence of the hydrophilic polymer.

In a further aspect of the invention, there is provided a precoatedprocessless radiation-imageable lithographic printing precursor,comprising a first layer of the radiation-sensitive medium of thepresent invention, precoated onto a substrate and dried, and an aqueouseluable hydrophilic overcoat, comprising at least one hydrophilicpolymer, precoated and dried onto the first layer.

In a further aspect of the invention there is provided a method formaking a precoated processless radiation-imageable lithographic printingprecursor, comprising the coating of the radiation-sensitive medium ofthe invention onto a substrate and drying the coated radiation-sensitivemedium, followed by the coating and drying of a aqueous eluablehydrophilic overcoat, comprising at least one hydrophilic polymer.

In yet a further aspect of the invention there is provided a method formaking a negative working lithographic printing master using theprecoated processless radiation-imageable lithographic printingprecursor. The precoated processless radiation-imageable lithographicprinting precursor may be imaged using absorbed radiation that isimagewise converted to heat, transforming hydrophilic areas tohydrophobic areas, resulting in areas of hydrophilic and areas ofhydrophobic property. This allows the latent image so formed to beemployed in making a negative-working lithographic printing master. Theimaging process is irreversible when performed. That is, the coated anddried radiation-sensitive medium remains hydrophobic after imagewiseexposure to imaging radiation. The method may be performed on aplate-setting machine or fully on-press.

DEFINITIONS

The term “negative-working lithographic printing master” is used hereinto describe a lithographic printing master on which, during the processof transferring printing ink from the master to a printing medium forreceiving printing ink, the printing ink adheres to those areas thatwere irradiated or written to in any way whatsoever by an imaging headand, conversely, on which printing ink does not adhere to those areasthat were not irradiated or written to in any way by that imaging head.Whether the master is referred to as negative-working orpositive-working is therefore not determined by the means of creatingink-bearing and non-ink-bearing areas on the master, but rather bywhether the positive image to be created on the printing medium forreceiving the printing ink, or the negative of it, respectively, istransferred to the master from the imaging head. In brief, on a“negative-working lithographic printing master”, those areas that arewritten by the imaging head will carry printing ink.

The phrase “processless radiation-imageable lithographic printingprecursor” is used herein to describe a radiation-imageable lithographicprinting precursor that requires no imagewise removal of, or imagewiseaddition to, any part of the precursor after imagewise exposure of theprecursor to radiation in order to form a lithographic printing master.

The phrase “precoated processless radiation-imageable lithographicprinting precursor” is used herein to describe a processlesslithographic printing precursor that comprises a radiation-sensitivemedium coated onto a substrate.

Substrates may specifically include printing press drums or sleeves, thedrums or sleeves being precoated with radiation-sensitive medium, orwith radiation-sensitive medium and an adhesion-promoting layer.

The term “eluent” refers to any fluid, either liquid or gaseous, whichis capable of dissolving or otherwise placing the unpatterned coating ofthe radiation-sensitive medium into a dispersible form.

The term “dispersible” means, with respect to a layer of given material,that the material is capable of displacement or removal, includinglifting off, by physical or chemical action of a fluid.

The term “aqueous eluable” is used to describe a property of an overcoatlayer coated over a aqueous ineluable radiation-sensitive layer, wherebythe hydrophilic overcoat layer, but not the aqueous ineluableradiation-sensitive layer, is removable by dissolving and/or dispersingit in an aqueous medium like water or fountain solution as used onprinting presses.

The term “aqueous-ineluable” is used to describe a property of aradiation-sensitive medium coated on a substrate, whereby theradiation-sensitive medium is not dissolved or otherwise dispersible byan aqueous eluent. It must be remembered that nearly any material may beetched or dissolved, so that this term applies only to fluids that areintended to be used in the treatment of the layer (e.g., water, lowalkaline content aqueous solutions, acidic solutions, aqueous solutionswith low amounts of organic compounds such as 10% isopropanol ormethoxypropanol, and other fountain solutions used on printing presses.)

The term saccharide is used herein as defined by IUPAC, being inclusiveof monosaccharides and di-, oligo- and polysaccharides, the di- oligo-and polysaccharides being made up of a plurality of monosaccharide unitslinked to each other by a glycosidic bond.

Composition of the Radiation-Sensitive Medium

In a first embodiment of the present invention, a radiation-sensitivemedium comprises a continuous phase and hydrophilic polymer particles.The hydrophilic polymer particles comprise a thermally softenablehydrophobic polymer, a hydrophilic polymer and a bonding compoundcapable of chemically bonding to the hydrophobic polymer and to thehydrophilic polymer. The polymer particles are made by polymerization ofat least one hydrophobic monomer and at least one bonding compound inthe presence of the hydrophilic polymer. The radiation-sensitive mediumof the present invention, when coated and dried, is aqueous-ineluableand a layer of the radiation-sensitive medium becomes hydrophobic whenimaged using absorbed radiation that is imagewise converted to heat. Asubstance capable of converting radiation into heat is preferably addedto the composition to create a suitably radiation-sensitive medium.

The hydrophilic polymer particles are hydrophilic to a substantialdepth, with only a core region of the particles being hydrophobic. A“substantial depth” means a depth that is sufficiently large that when alithographic printing master made from a coated precursor in accordancewith the invention is employed in printing, the hydrophilic areas of thecoating will not erode sufficiently to expose the hydrophobic core ofthe particles and thereby detrimentally affect printing quality to amaterial degree. Being hydrophilic to a substantial depth stands incontrast to the various particle types discussed in U.S. Pat. No.6,653,042, which are either entirely hydrophilic or have only asuperficial hydrophilic surface region or coating. The polymer particlesof the present invention are distinctly hydrophilic, compared with thehydrophobic particles disclosed in U.S. Pat. No. 6,550,237. Thehydrophilic particles are also to be contrasted with the materialsdisclosed in U.S. Pat. No. 5,569,573 (Takahashi et al.) and EP 0 949 088A1 (Tanaka et al.) which are both microcapsuled materials. Withoutwishing the invention to be limited in any way, the inventors believethat the cores of the particles are dominated by the hydrophobic polymerderived from the hydrophobic monomer, while the rest of any givenparticle is dominated by the hydrophilic polymer. It is believed thatthere is a transition region wherein there are copolymers of both thehydrophobic monomer and the hydrophilic polymer with the bondingcompound (itself preferably hydrophilic as a polymer), producing therebya particle that has three regions, namely, an inner hydrophobic core, atransition region that is largely hydrophilic, due to the nature of thepreferred bonding compounds, and the rest of the particle, beingdominated by the hydrophilic polymer.

The hydrophobic monomer of the present invention is selected fromelectrically neutral ethylenically unsaturated monomers such asethylene, propylene, styrene, other vinyl monomers (e.g. methylmethacrylate), and electrically neutral derivatives of theseethylenically unsaturated monomers. The term “electrically neutral” iswell understood in the art and includes primarily non-polar compounds,although monomers with internal charge distributions and overallelectrical neutrality (e.g., Zwitterions) are acceptable.

The bonding compound of the present invention is preferably selectedfrom within the classes of water-soluble/dispersible ethylenicallyunsaturated monomers, especially acryloyl or methacryloyl monomers andanionic-substituted styrene monomers, and especially acryloyl acids(i.e., acrylic acid, and methacrylic and other substituted acrylicacids) and sulfonated or phosphonated styrenes (e.g., with alkali oralkaline metal or ammonium counterions such as Na, Li, K and the like).

The hydrophilic polymer of the present invention is preferably selectedfrom chitosan polymers (which includes derivatized chitosan as describedherein), polyethyleneimine resins, polyamine resins (for examplepolyvinylamine polymers, polyallylamine polymers, polydiallylamineresins and amino(meth)acrylate polymers), polyamide resins,polyamide-epichlorohydrin resins, polyamine-epichlorohydrin resins,polyamidepolyamine-epichlorohydrin resins, as well asdicyandiamide-polycondensation products (for example,polyalkylenepolyamine-dicyandiamide copolymers). These polymers may beemployed alone or in a mixture or copolymer of two or more thereof. Thepolymers preferably have a molecular weight of 5,000 to 500,000, morepreferably 5,000 to 200,000. The content of hydrophilic polymer ispreferably 5 to 65% by weight, based on the total weight of theimageable layer.

The hydrophilic polymer of the present invention may also comprisesaccharides, such as cellulose or starch, or a mixture of suchsaccharides. The present invention allows for the hydrophilic polymer tobe comprised of a mixture of hydrophilic cationic resins andsaccharides. Furthermore, the hydrophilic polymer of the presentinvention may be a derivative of a saccharide and mixtures thereof withany one or more other hydrophilic cationic resin and saccharide.

In one embodiment of the invention, the coatable compositions compriselatices in aqueous carriers, the latices comprising dissolved chitosanand particles comprised of thermally softenable hydrophobic polymer,hydrophilic polymer and the bonding compound, bonding the hydrophobicpolymer and the hydrophilic polymer. In this embodiment, therefore,there is dissolved chitosan present, in addition to chitosan that may bethe hydrophilic polymer of the hydrophilic polymer particles. Thecomposition may also contain additives to assist in the imaging stepsand/or the coating steps. For example, a substance capable of convertingthe imaging radiation into heat is particularly desirable in thecompositions so that the imaging radiation is efficiently absorbed andconverted to heat to assist in the softening and coalescing of thepolymer particles. The composition preferably contains at least 0.05 to10% by weight of solids of a substance capable of converting radiationto heat. The substance capable of converting radiation to heat may be apigment, such as, but not limited to, carbon black, or a dye. Infraredand near infrared (NIR) dyes are particularly suitable for use withinfrared (IR) lasers.

In a preferred embodiment of the present invention the substance capableof converting radiation to heat absorbs radiation over the range 700 nmto 1200 nm, more preferably over the range 800 nm to 1100 nm, and mostpreferably over the range 800 nm to 850 nm, and converts it to heatExamples of such substances are disclosed in JOEM Handbook 2 AbsorptionSpectra of Dyes for Diode Lasers, Matsuoka, Ken, bunshin Shuppan, 1990and Chapter 2, 2.3 of Development and Market Trend of FunctionalColouring Materials in 1990's, CMC Editorial Department, CMC, 1990, suchas polymethine type coloring material, a phthalocyanine type coloringmaterial, a dithiol metallic complex salt type coloring material, ananthraquinone type coloring material, a triphenylmethane type coloringmaterial, an azo type dispersion dye, and an intermolecular CT coloringmaterial. The representative examples includeN-[4-[5-(4-dimethylamino-2-methylphenyl)-2,pentadienylidene]-3-methyl-2,5-cyclohexadiene-1-ylidene]-N,N-dimethylammoniumacetate,N-[4-[5-(4-dimethylaminophenyl)-3-phenyl-2-pentene-4-in-1-ylidene]-2,5-cyclohexadiene-1-ylidene]-N,N-dimethylammoniumperchlorate,bis(dichlorobenzene-1,2-dithiol)nickel(2:1)tetrabutyl-ammonium andpolyvinylcarbazol-2,3-dicyano-5-nitro-1,4-naphthoquinone complex. Somespecific commercial products that may be employed as substance capableof converting radiation to heat include Pro-jet 830NP, a modified copperphthalocyanine from Avecia of Blackley, Lancashire in the U.K., ADS830A, an infra-red absorbing dye from American Dye Source Inc. ofMontreal, Quebec, Canada, and S0094, S0306, S0391 and S0451, allinfrared absorbing dyes from FEW Chemicals GmbH of Wolfen, Germany.Hydrophobic forms of these dyes are particularly preferred as thisproperty makes these dyes more compatible with the hydrophobic aspect ofthe particles, thereby facilitating heat transfer to the thermallysoftenable hydrophobic polymer when radiation is being absorbed and heatproduced during irradiation of the medium coated on a lithographic base.

Cosolvents (e.g., alcohols, ketones, and other organic solvents),surfactants, blowing agents, and filler (e.g., silica, titania, zincoxide, zirconia, etc.) are also useful additives, and may be present innon-limiting exemplary amounts of up to 25% by weight of total solids,and the like. The use of filler particles, preferably having volumeaverage particle sizes of between 0.01 to 0.5 micrometers, and less than50% of the volume average size of the polymeric particles, isparticularly desirable. Especially when using inorganic fillerparticles, such as metal or semimetal oxides or silica, the particlescan acid a surprisingly higher level of on-press durability tolithographic printing masters prepared from the radiation-sensitivemedium of the present invention.

Preferably, the polymer or polymers that constitute the thermallysoftenable hydrophobic polymer component of the particles have a filmforming temperature above ambient temperature (e.g., 20° C.) and maycomprise any thermally softenable or heat-fusible polymer, and, by wayof non-limiting examples, may be an addition polymer comprising residuesderived from one or more of styrene, substituted styrenes, esters of(meth)acrylic acid, vinyl halides, (meth)acrylonitrile, vinyl esters,silicon-containing polymerizable monomers or polyethers. It may also bea polyester, polyamide or polyurethane, or any thermally fusibleoleophilic material or composition capable of forming a hydrophobiccenter/hydrophilic outer layer structure by polymerization with one ormore anionic monomers. Preferred materials are addition polymerscontaining 50% or more by weight of styrene or substituted styrenes.Most preferred materials are polymers containing 50% or more by weightof esters of (meth)acrylic acid. The hydrophobic centers of the polymerparticles preferably soften at temperatures such as from 30° C. to 30°C., and more preferably from 60° C. to 200° C. to allow coalescence,flow, phase change or any other phenomenon to occur within or betweenthe particles to effect the hydrophilicity decrease In the surface ofthe layer. Suitable examples of esters of (meth)acrylic acid include,but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate,propyl (meth)acrylate, butyl (meth)acrylate and lauryl (meth)acrylate.Suitable examples of substituted styrenes include, but are not limitedto, alpha-methylstyrene and vinyltoluene. Suitable examples ofsubstituted vinyl esters include, but are not limited to, vinyl acetateand vinyl propionate. Suitable examples of vinyl halides include, butare not limited to, vinyl chloride and vinylidene chloride.

Co-monomers used with these monomers may include up to 50% by weight ofpolymerizable monomers having carbon-carbon double bonds including, butnot limited to monomers having various types of carboxyl groups, such asacrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaricacid, maleic acid, citraconic acid and their salts; monomers havingvarious types of hydroxyl groups, such as 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate,monobutylhydroxyl fumarate and monobutylhydroxyl itaconate; varioustypes of nitrogen-containing vinyl monomers such as (meth)acrylamides,diacetone acrylamides, N-methylol acrylamides; sulphonamide- orphosphorus-containing vinyl monomers; various types of conjugated dienessuch as butadiene; dicarboxylic acid half-esters of hydroxylgroup-containing polymers, such as phthalic, succinic or maleic acidhalf esters of a polyvinyl acetal and, in particular, of a polyvinylbutyral; and alkyl or aralkyl half esters of styrene- or alkyl vinylether-maleic anhydride copolymers, in particular alkyl half esters ofstyrene-maleic anhydride copolymers.

In a preferred embodiment of the invention, the hydrophilic polymer ischitosan, which is normally prepared from chitin. Chitosan, anaminopolysaccharide, is bio-friendly. Despite its abundance in nature,chitin has not been effectively utilized because of its low solubilityin aqueous solutions. Owing to this problem, chitin is difficult to forminto fibers or films and thus, has found limited applications. In aneffort to overcome this problem, chitin is often converted intochitosan. A deacetylation technique is generally used for the conversionof chitin into chitosan. U.S. Pat. No. 3,633,940 discloses a method forpreparing chitosan from chitin, along with its application to fibers andfilms. For possible applications, the prepared chitosan is dissolved inaqueous organic solutions.

Chitosan may be provided in the practice of the present invention in awide range of properties as long as its hydrophilic surface propertiesare maintained. A non-limiting example of the types of chitosan that areparticularly useful in the practice of the invention are chitosan whichranges in molecular weight from 5,000 to 500,000, more preferably 5,000to 200,000, and in deacetylation degree from 60 to 99%, more preferablyfrom 70 to 95%. The chitosan also provides an emulsifying agent for thethermally softenable or fusible polymer particles when in the coatingcomposition.

Synthesis of the Radiation-Sensitive Medium

A preferred mode of synthesis of the radiation-sensitive medium of thepresent invention is performed via the following steps, illustrated by,but not limited to, the use of chitosan as hydrophilic polymer. Thehydrophilic polymer is dissolved in a suitable solvent and thehydrophobic monomer is added. An initiator may be added in either ofthese steps. The resultant mixture is polymerized by heating. Thebonding compound may be added either during or after the polymerizationof the hydrophobic monomer. The substance capable of convertingradiation to heat is added prior to coating. Minor amounts ofco-solvents, blowing agents, fillers and surfactants may be added atvarious stages of the synthesis.

Any solvent may be used that dissolves the chitosan and not thehydrophobic monomer, selected from aqueous acidic solutions, aqueousinorganic salt solutions and organic solvents. To obtain an aqueousacidic solution, which is a desired route In practicing the invention,water is added with 0.1-20 wt % of an acid, which is selected from thegroup consisting of organic acids, such as acetic acid and lactic acid,and inorganic acids, such as hydrochloric acid. Available inorganic saltsolutions that can assist in the dissolving of chitosan include, by wayof non-limiting examples, an inorganic salt at an amount of 10-70 wt %in water. The inorganic salt is particularly desirably selected from thegroup consisting of alkali metal (e.g., sodium) thiocyanate, metalchlorides (e.g., zinc chloride, calcium chloride, sodium chloride,potassium chloride, lithium chloride, and mixtures thereof). Organicsolvents that may be useful in carrying the dissolved chitosan in thepresent invention are polar, examples of which includedimethylacetamide, N-methylpyrrolidone, dimethylformamide,diethylacetamide, trifluoroacetic acid, trichloroacetic acid, andmixtures thereof. In order to obtain higher polarity, one or moreselected from the above-mentioned inorganic metal salts may be added atan amount of 0.1-10 wt % to the organic solvent.

The polymerization process can be effected as described by Wen-Yen Chiuet al. in Journal of Polymer Science A (Polymer Chemistry) volume 39,2001, pp 1646-1655. The co-monomer, e.g. (meth)acrylic acid, can becopolymerized with the primary component of the hydrophobic polymercomposition, e.g. styrene or methyl methacrylate. In the polymerizationprocess, an initiator (e.g., persulfate-metabisulfite) must be present.Other commonly known initiators for radical polymerization can also beused to give satisfactory polymers as described by Odian in Principlesof Polymerization, 3d Edition, publisher John Wiley & Sons, NY (1991) pp212-215, 219-225 and 229-232.

The post-polymerization mix may generally comprise the following:

-   -   solvent (40-97 w/w % of total mix)    -   excess dissolved hydrophilic solubilizable polymer (0.01-50 w/w        % of total mix)    -   particles comprising electrically neutral hydrophobic polymer        (2-59 w/w % of total mix)

The post-polymerization mix comprises a continuous phase and a dispersedphase, the dispersed phase comprising 50-99.9w/w % of polymerizedelectrically neutral hydrophobic monomer and 0.1-50 w/w % polymerizedanionic monomer. The post-polymerization mix may contain suspendedsolids in the size range from 0.01 to 5 microns.

Minor amounts of additives may be added at various stages of thepolymerization or particle formation process. Surfactants can be added(e.g., silicone-polyether,) to improve film forming quality when thecomposition is coated onto a surface. A plasticizer may be added at anytime before coating of the composition, but is preferably present wellbefore the coating to allow it to mix with the polymer.

In a further step 0.05 to 10 w/w % of solids of the substance capable ofconverting radiation into heat is added. Other additives, including theco-solvents, surfactants, blowing agents and fillers, can be added inamounts from 0-25 w/w % of solids.

Aqueous Eluable Hydrophilic Overcoat

The lithographic printing plate precursor of the present inventionpreferably comprises an aqueous eluable hydrophilic overcoat provided onthe heat-sensitive hydrophilic layer to improve the overall performanceof the lithographic printing plate. The inventors have found that anaqueous-soluble or aqueous-dispersible hydrophilic overcoat on top ofthe heat-sensitive hydrophilic layer will prevent the surface of theheat-sensitive layer from being contaminated and/or scratched duringstorage and/or handling. The aqueous-soluble or aqueous-dispersiblehydrophilic overcoat provided an the heat-sensitive hydrophilic layer ofthe lithographic printing plate precursor also significantly improvesstart-up on press. A further benefit stems from the fact that theovercoat provides a higher optical reflectivity value, which isparticularly useful in platesetter systems that employ an autofocusarrangement to focus the imaging radiation on the imageable layer. Sincemany lithographic printing plate precursors tend to exhibit changes incharacteristics With time, temperature and humidity, the overcoat alsohelps in minimizing these effects.

As the lithographic printing plate precursor of the invention does notrequire a wet processing step after exposure, the hydrophilic overcoateluable in aqueous media has been designed to be easily removable, atleast in the imaged areas, during start-up on press. Some of thespecific requirements taken into consideration during the design, werethe eluability in water or fountain, a high thermal stability to ensureminimal thermal degradation during imaging, minimal compatibility withthe heat-sensitive hydrophilic layer to allow rapid removal, chemicalinertness to satisfy product shelf life requirements. The overcoat thuscomprises a resin, or a mixture of resins, selected from the group ofwater-soluble organic polymers.

Representative examples of these resins include polyvinylalcohol,polyvinylacetate, polyacrylic acid, poly(meth)acrylic acid or its alkalimetal salt and amine salt, poly 2-hydroxyethyl(meth)acrylate,poly(meth)acrylamide, polyvinyl methyl ether, polyvinyl methylether/maleic anhydride copolymer, polyvinylpyrollidone,poly-2-acrylamide-2-methylpropane sulfonic acid and alkali metal oramine salt thereof, alginic acid or its salts, protan jelly, carageenin,tragacanth, laminarin sulfate, starch, animal glues, vegetablemucilages, gum arabic, cellulose and modification product thereof,polysaccharides such as dextran, pullulan, or chitosan. The termsaccharide is used herein as defined by IUPAC, being inclusive ofmonosaccharides and di-, oligo- and polysaccharides, the di-, oligo- andpolysaccharides being made up of a plurality of monosaccharide unitslinked to each other by a glycosidic bond.

The aqueous eluable hydrophilic overcoat may comprise additionalingredients, such as a second polymer, a plasticizer to give the coatingflexibility and reduce cracking, a light-to-heat-converting agent tocounteract any speed loss due to the additional coating thickness, asurfactant or wetting agent to improve coatability, a water-solublevisible dye or colorant to help with the QC of the hydrophilic overcoat,and a highly water-soluble crystalline compound to accelerate thebreakdown of the structural integrity of the overcoat during roll-up onpress. The aqueous eluable hydrophilic overcoat may also compriseingredients, such as small carboxylic acid molecules (e.g citric acid),polyvinylphosphonates, and other materials commonly found in platestorage gum solutions, e.g. phosphates, sodium hexametaphosphate, sodiumgluconate, tartaric acid. Representative examples of suitableplasticizers are ethylene glycol, glycerin, sorbitol,carboxymethylcellulose.

Preferably, the light-to-heat converting agent is a water-soluble IRdye, for example, a water-soluble cyanine dye as described in U.S. Pat.No. 6,159,657, U.S. Pat. No. 6,397,749, U.S. Pat. No. 6,410,202, or ascommercially available from FEW Chemicals, but other IR-absorbing dyesmay be used as well. Acid Green 25 is one example for a usefulwater-soluble visible dye. Useful examples of highly water-solublecrystalline compounds have been described in U.S. Pat. No. 5,677,110. Anespecially preferred highly water-soluble crystalline compound isglucose.

The coating weight of the aqueous eluable hydrophilic overcoatpreferably is 0.5 g/m² or less. More preferably the coating weight is0.1 g/m² or less. Most preferably the coating weight of the overcoat isbetween 0.01 and 0.05 g/m². This coating weight of the protective layeris low enough not to negatively affect the oleophilicity of the imagedareas or to result in a significant increase of the exposure energyrequired for optimum image formation.

Water-soluble overcoats applied to radiation-sensitive layers arewell-known in the industry, but need to be designed for the particularapplication or medium to be coated. It is not obvious that overcoatspreviously disclosed will function appropriately for the presentaqueous-ineluable coating of radiation-sensitive medium. One example isthat of U.S. Pat. No. 6,513,433 (Inoue. et al.) Inoue et al. describes awater soluble overcoat layer provided on the heat sensitive layer ofthat patent. However, the particular heat sensitive layer of U.S. Pat.No. 6,513,433 is of a different composition, functions by a totallydifferent mechanism from that employed in the present invention, and,additionally, is removed by the on-press fountain solution in theunexposed areas. In contrast, the aqueous-ineluable coating ofradiation-sensitive medium of the present invention is not removed inthe unexposed areas.

Preparation of the Precoated Processless Radiation-ImageableLithographic Printing Precursor

The radiation-sensitive medium is applied to a substrate and dried bythe standard coating and drying methods employed in the manufacture ofprinting plate precursors and other metal, plastic, ceramic and paperproducts, to create a radiation-imageable layer. Similarly, after thelayer of radiation-sensitive medium has been applied and dried, theaqueous eluable hydrophilic overcoat may be applied and dried usingstandard coating and drying methods. The two coatings, however, do nothave to use the same coating or drying techniques. The dryingtemperature for the protective aqueous eluable hydrophilic overcoatpreferably is low enough not to cause any negative effects on the coatedand dried radiation-imageable layer. For example if the dryingtemperature of the aqueous eluable hydrophilic overcoat is too high(more than 100° C.) a bleaching of the coated and driedradiation-imageable layer may be observed. The substrate material useddepends upon the purpose for which the image is to be used and may be,for example, formed of metal, polymer material (such as, but not limitedto, PET), paper, ceramic, or composite material. The substrate ispreferably aluminum and more preferably chemically treated aluminum,grained aluminum, anodized aluminum, aluminum coated substrates, orcombinations thereof. Preferably, the substrate is sufficiently flexibleto facilitate mounting on presses. To the extent that the precoatedprocessless radiation-imageable lithographic printing precursor of thepresent invention does not require any water carrying or water adhesivequality from the substrate, the substrate being not exposed duringprinting, there is wide scope of choice for the materials of which thesubstrate may be composed.

According to another embodiment in connection with the presentinvention, the substrate comprises a flexible support, such as e.g.paper or plastic film, provided with a further adhesion-promoting layerof cross-linked polymer. A suitable cross-linked hydrophilic layer maybe obtained from a hydrophilic (co-) polymer cured with a cross-linkingagent such as a hydrolysed tetra-alkylorthosilicate, formaldehyde,glyoxal or polyisocyanate. Particularly preferred is the hydrolysedtetra-alkylorthosilicate. For the purposes of the present invention,this layer must be capable of being wetted by the radiation-sensitivemedium to give a good quality of coating and is therefore usuallyhydrophilic. The hydrophilic (co-) polymers that may be used comprisefor example, homopolymers and copolymers of vinyl alcohol, hydroxyethylacrylate, hydroxyethyl methacrylate, acrylic acid, methacrylic acid,acrylamide, methylol acrylamide or methylol methacrylamide. Thehydrophilicity of the (co-) polymer or (co-) polymer mixture used ispreferably higher than that of polyvinyl acetate hydrolyzed to at leastan extent of 60 percent by weight, preferably 80 percent by weight.

In a further embodiment of the invention, an adhesion-promoting layer iscoated on the substrate. Suitable adhesion-promoting layers for use inaccordance with the present invention comprise a hydrophilic (co-)polymer binder and colloidal silica as disclosed in EP 619524, and EP619525. Preferably, the amount of silica in the adhesion-promoting layeris between 0.2 and 0.7 mg per m². Further, the ratio of silica tohydrophilic (co-) polymer binder is preferably more than 1 and thesurface area of the colloidal silica is preferably at least 300 m² pergram.

Preparation of the Negative-Working Lithographic Printing Master

The preparation of the negative-working lithographic printing master maybe performed on a platesetter machine or directly on the printing press.In both cases, the precoated processless radiation-imageablelithographic printing precursor of the invention may be mounted on theplatesetter or printing press. Alternatively, in the case of eithermachine, the radiation-sensitive medium and the aqueous eluablehydrophilic overcoat may be applied to the substrate and to the coatedand dried first layer of radiation sensitive medium while the substrateresides on the relevant machine. The substrate may be an integral partof the press or it may be removably mounted on the press. In thisembodiment, the imageable coating may be dried by means of a curing unitintegral with the press, as described in U.S. Pat. No. 5,713,287(Gelbart). It is also possible to coat a cylinder of a printing presswith a layer of radiation-sensitive medium when the cylinder is separatefrom the press. Before applying the imageable coating to the substrate,the substrate may be treated to enhance the adhesion of the imageablecoating.

In a preferred embodiment of the invention, the radiation-sensitivemedium of the coating is imagewise converted by means of the spatiallycorresponding imagewise generation of heat within the coating to form ahydrophobic area corresponding to areas imagewise irradiated. Theimaging process itself may be by means of scanned laser radiation asdescribed in U.S. Pat. No. 5,713,287. The wavelength of the laser lightand the absorption range of the converter substance are chosen to matcheach other. The heat to drive the process of converting the irradiatedareas of the precursor from hydrophilic to hydrophobic is produced viathe substance capable of converting radiation into heat. Theradiation-sensitive medium of the present invention, when coated anddried on a suitable substrate, therefore becomes hydrophobic under theaction of heat. The aqueous eluable hydrophilic overcoat of theprecursor remains largely unaffected in this imaging process. Duringsubsequent wet lithographic offset printing, the on-press fountainsolution, being an aqueous medium, removes the aqueous eluablehydrophilic overcoat, at least in the imaged areas, to expose theunderlying layer of image-wise irradiated imageable coating for use inprinting. Any small amounts of aqueous eluable hydrophilic overcoatremaining in the unimaged areas after such treatment with fountainsolution do not constitute a problem in printing, since theaqueous-ineluable coating of a radiation-sensitive medium in that arearemains hydrophilic anyway.

The exposed areas of the imageable coating will be hydrophobic and thelithographic printing ink will adhere preferentially to these areas, aswater or fountain solution will be adhering to the hydrophilic areas.This makes the processless printing master of the present inventioninherently negative-working. The method does not require a substrate ofcontrolled hydrophilicity and provides great toughness in the exposedareas of the precursor, thereby extending the run length of thenegative-working lithographic printing master. The aqueous eluablehydrophilic overcoat assures a trouble-free startup on press, even forplates that have aged.

Without limiting the scope of the invention in any way, the mechanism bywhich the irradiated areas of the layer become hydrophobic is believedto be as follows. When the radiation-imageable layer is imaged, thesubstance capable of converting radiation into heat provides imagewisedistributed heat. This imagewise distributed heat provides theactivation energy required to turn the imageable layer from, what theinventors believe to be, a metastable state into a thermodynamicallystable state. The majority of the copolymer is the thermally softenablehydrophobic polymer. However, when the imageable layer is coated anddried, the particles are locked into a metastable state in which themore hydrophilic surface regions of the polymer particles dominate thesurface energy, rendering the layer hydrophilic. It is believed thatthis happens because the coating occurs out of a highly polar solventmix, which favors the hydrophilic state. After drying, the solvents areremoved, but the solids remain in the metastable hydrophilic state. Uponexposure to radiation that gets converted to heat by the substancecapable of converting radiation into heat, the required activatingenergy is provided for the polymer particles in the exposed areas torelax to the thermodynamically stable hydrophobic state and at leastpartially coalesce. In the unirradiated areas, where the activatingenergy has not been provided, the coated layer remains hydrophilic.During wet offset printing, the irradiated regions form theink-accepting image-areas, whereas the unirradiated areas of the layerremain hydrophilic and take fountain solution, thereby being adhesive toink.

The imaging process is irreversible when performed. The areas of thecomposition exposed to imaging radiation remain hydrophobic and cannotbe reversed to form a useable processless radiation-imageablelithographic printing precursor by way of thermal treatment (heating orcooling), radiation treatment to the same or different imaging range ofradiation. The composition and radiation-sensitive medium isaqueous-ineluable when coated and dried and is specifically notremovable by water or fountain-solution when coated and dried.

As is evident, the radiation-sensitive medium and lithographic printingprecursors of the present invention allow the combination of thebenefits of the newer generation of polymer particle/coalescence-type ofthermally sensitive media with the substrate-independence of aswitchable polymer approach to plate-making. With the particles having asubstantially hydrophilic nature, rather than merely superficial, thereis also reduced scumming, a phenomenon that occurs when thewater-bearing area of the master loses some of its hydrophilic natureand starts to take ink. This provides a master with excellentrun-length, which is nevertheless producible from an aqueous basedradiation-sensitive medium.

EXAMPLES

All materials used in the following examples are readily available fromstandard commercial sources, such as Aldrich Chemical Co. (Milwaukee,Wis.), Polysciences, Inc. (Warrington, Pa.) or VWR Canlab, (Mississauga,Canada), unless otherwise specified.

Chitosan was obtained as “High Viscosity Chitosan” from Vanson, Redmond,Wash., USA or as “Chitosan” from Primex, Siglufjordur, Iceland.

The infrared dyes are S0094 and S0391 from FEW Chemicals GmbH in Wolfen,Germany.

The wetting agent is BYK-345 from BYK-Chemie, Wallingford, Conn., USA.

Triton X-405 was obtained from Dow Chemical Company, Midland, Mich.,USA.

Gum Arabic was obtained as “100% Pure Gum Arabic” from Anchor, OrangePark, Fla., USA.

All infrared laser exposure was at 830 nm wavelength using a CreoTrendsetter™ platesetting machine.

Example 1

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PS copolymer (13 wt % Chitosan and 87% Styrene) aqueousdispersion with 10% solids in aqueous and 9 g of 2 wt % infrared dye inethanol. After drying at room temperature for 5 minutes, the plate wasimaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Ryobi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 1000impressions were printed on coated paper with little deterioration ofprinting quality. During printing, the surface on background remainsunchanged.

Example 2

A plate was produced by coating the following formulation on toungrained, unanodized aluminum plate to give a dry coating weight of 1g/m²: 30 g Chitosan/PS copolymer (13 wt % Chitosan and 87% Styrene)aqueous dispersion with 10% solid and 9 g of 2 wt % infrared dye inethanol. After drying at room temperature for 5 minutes, the plate wasimaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Ryobi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 1000impressions were printed on coated paper with little deterioration ofprinting quality. During printing, the surface on background remainsunchanged.

Example 3

A plate was produced by coating the following formulation on to aCeramic Paper to give a dry coating weight of 1 g/m² 30 g Chitosan/PScopolymer (13 wt % Chitosan and 87% Styrene) aqueous dispersion with 10%solid and 9 g of 2 wt % infrared dye in ethanol. After drying at roomtemperature for 5 minutes, the plate was imaged using infrared laserexposure of 500 mJ/cm² at 15 Watts. The imaged sample was mounted onto apress (Ryobi), dampened with fountain solution for 30 seconds before theink was applied to the plate. 3000 impressions were printed on coatedpaper with little deterioration of printing quality. During printing,the surface on background remains unchanged.

Example 4

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PS/AN copolymer (13 wt % Chitosan, 78% Styrene, 9%Acrylonitile) aqueous dispersion with 10% solid and 9 g of 2 wt %infrared dye in ethanol. After drying at 60° C. for 2 minute, the platewas imaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Multi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 1000impressions were printed on uncoated paper, During printing, the surfaceon background remains unchanged.

Example 5

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PS/AA copolymer (13 wt % Chitosan, 78% Styrene, 9% Acrylicacid) aqueous dispersion with 10% solid and 9 g of 2 wt % infrared dyein ethanol. After drying at 60° C. for 2 minutes, the plate was imagedusing infrared laser exposure of 500 mJ/cm² at 15 Watts. The imagedplate was mounted onto a press (Multi), dampened with fountain solutionfor 30 seconds before the ink was applied to the plate. 5000 impressionswere printed on uncoated paper. During printing, the surface onbackground remains unchanged.

Example 6

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:15 g Gelatin/PS/AN copolymer (13 wt % Gelatin, 78% Styrene, 9%Acrylonitrile) aqueous dispersion with 10% solid and 15 gChitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methyl methacrylate,9% Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2 wt %infrared dye in ethanol. After drying at 60° C. for 2 minutes, the platewas imaged using Infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Multi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 5000impressions were printed on uncoated paper. During printing, the surfaceon background remains unchanged.

Example 7

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:15 g Starch/PS/AN copolymer (13 wt % Starch, 718% Styrene, 9%Acrylonitrile) aqueous dispersion with 10% solid and 15 gChitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methyl methacrylate,9% Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2 wt %infrared dye in ethanol. After drying at 60° C. for 2 minutes, the platewas imaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Multi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 5000impressions were printed on uncoated paper. During printing, the surfaceon background remains unchanged.

Example 8

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:24 g Chitosan/PS copolymer (13 wt % Chitosan and 87% Styrene) aqueousdispersion with 10% solid and 6 g Chitosan/PMMA/A copolymer (13 wt %Chitosan, 78% Methyl methacrylate, 9% Acrylic acid) aqueous dispersionwith 10% solid and 9 g of 2 wt % infrared dye in ethanol. After dryingat 60° C. for 2 minutes, the plate was imaged using infrared laserexposure of 500 mJ/cm² at 15 Watts. The imaged plate was mounted onto apress (Multi), dampened with fountain solution for 30 seconds before theink was applied to the plate. 1000 impressions were printed on uncoatedpaper. During printing, the surface on background remains unchanged.

Example 9

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:24 g Chitosan/PS/AN copolymer (13 wt % Chitosan, 78% Styrene, 9%Acrylonitrile) aqueous dispersion with 10% solid and 6 gChitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methyl methacrylate,9% Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2 wt %infrared dye in ethanol. After drying at 60° C. for 2 minutes, the platewas imaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Multi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 1000impressions were printed on uncoated paper. During printing, the surfaceon background remains unchanged.

Example 10

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PS/AA copolymer (13 wt % Chitosan, 78% Styrene, 9% Acrylicacid) aqueous dispersion with 10% solid and 9 g of 5 wt % carbon black(CAB-O-JET 200) in water. After drying at 60° C. for 2 minutes, theplate was imaged using infrared laser exposure of 800 mJ/cm² at 15Watts. The imaged plate was mounted onto a press (Multi), dampened withfountain solution for 30 seconds before the ink was applied to theplate. 1000 impressions were printed on uncoated paper. During printing,the surface on background remains unchanged.

Example 11

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Starch/PS/AA copolymer (13 wt % starch, 78% Styrene, 9% Acrylicacid) aqueous dispersion with 10% solid and 9 g of 2 wt % infrared dyein ethanol. After drying at 60° C. for 2 minutes, the plate was imagedusing infrared laser exposure of 500 mJ/cm² at 15 Watts. The imagedplate was mounted onto a press (Multi), dampened with fountain solutionfor 30 seconds before the ink was applied to the plate. 500 impressionswere printed on uncoated paper. During printing, the surface onbackground remains unchanged.

Example 12

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Gelatin/PS/AA copolymer (13 wt % Gelatin, 78% Styrene, 9% Acrylicacid) aqueous dispersion with 10% solid and 9 g of 2 wt % infrared dyein ethanol. After drying at 60° C. for 2 minutes, the plate was imagedusing infrared laser exposure of 500 mJ/cm² at 15 Watts, The imagedplate was mounted onto a press (Multi), dampened with fountain solutionfor 30 seconds before the ink was applied to the plate. 500 impressionswere printed on uncoated paper. During printing, the surface onbackground remains unchanged.

Example 13

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Cellulose/PS/AA copolymer (13 wt % Cellulose, 78% Styrene, 9%Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2 wt %infrared dye in ethanol, After drying at 60° C. for 2 minutes, the platewas imaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Multi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 500impressions were printed on uncoated paper. During printing, the surfaceon background remains unchanged.

Example 14

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PMMA/AA copolymer (13 wt % Chitosan, 78% Methylmethacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 gof 2 wt % infrared dye in ethanol. After drying at 60° C. for 2 minutes,the plate was imaged using infrared laser exposure of 500 mJ/cm² at 15Watts. The imaged plate was mounted onto a press (Multi), dampened withfountain solution for 30 seconds before the ink was applied to theplate-1000 impressions were printed on uncoated paper. During printing,the surface on background remains unchanged.

Example 15

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PS/PMMA/AA copolymer (13 wt % Chitosan, 39% Styrene, 36%Methyl methacrylate, 9% Acrylic acid) aqueous dispersion with 10% solidand 9 g of 2 wt % infrared dye in ethanol. After drying at 60° C. for 2minutes, the plate was imaged using infrared laser exposure of 500mJ/cm² at 15 Watts, The imaged sample was mounted onto a press (Multi),dampened with fountain solution for 30 seconds before the ink wasapplied to the plate. 500 impressions were printed on uncoated paper.During printing, the surface on background remains unchanged.

Example 16

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:25 g Chitosan/PS/AA copolymer (13 wt % Chitosan, 78% Styrene, 9% Acrylicacid) aqueous dispersion with 10% solid, 5 g of 10% Zinc oxide inethanol and 9 g of 2 wt % infrared dye in ethanol. After drying at 60°C. for 2 minutes, the plate was imaged using infrared laser exposure of500 mJ/cm² at 15 Watts. The imaged plate was mounted onto a press(Multi), dampened with fountain solution for 30 seconds before the inkwas applied to the plate. 500 impressions were printed on uncoatedpaper. During printing, the surface on background remains unchanged.

Example 17

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:25 g Chitosan/PS/AA copolymer (13 wt % Chitosan, 78% Styrene, 9% Acrylicacid) aqueous dispersion with 10% solid 5 g of 10% SiO₂ in ethanol and 9g of 2 wt % infrared dye in ethanol. After drying at 60° C. for 2minutes, the plate was imaged using infrared laser exposure of 500mJ/cm² at 15 Watts. The imaged plate was mounted onto a press (Multi),dampened with fountain solution for 30 seconds before the ink wasapplied to the plate. 5000 impressions were printed on uncoated paper.During printing, the surface on background remains unchanged.

Example 18

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PnBMA/AA copolymer (13 wt % Chitosan, 78% n-butylmethacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 gof 2 wt % infrared dye in ethanol. After drying at 60° C. for 2 minutes,the plate was imaged using infrared laser exposure of 500 mJ/cm² at 15Watts. The imaged plate was mounted onto a press (Multi), dampened withfountain solution for 30 seconds before the ink was applied to theplate. 1000 impressions were printed on uncoated paper. During printing,the surface on background remains unchanged.

Example 19

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PtBMA/AA copolymer (13 wt % Chitosan, 78% t-Butylmethacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 gof 2 wt % infrared dye in ethanol. After drying at 60° C. for 2 minutes,the plate was imaged using infrared laser exposure of 500 mJ/cm² at 15Watts. The imaged plate was mounted onto a press (Multi), dampened withfountain solution for 30 seconds before the ink was applied to theplate. 1000 impressions were printed on uncoated paper. During printing,the surface on background remains unchanged.

Example 20

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PEMA/AA copolymer (13 wt % Chitosan, 78% Ethylmethacrylate, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 gof 2 wt % infrared dye in ethanol. After drying at 60° C. for 2 minutes,the plate was imaged using infrared laser exposure of 500 mJ/cm² at 15Watts. The imaged plate was mounted onto a press (Multi), dampened withfountain solution for 30 seconds before the ink was applied to theplate. 500 impressions were printed on uncoated paper. During printing,the surface on background remains unchanged.

Example 21

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PtBS/AA copolymer (13 wt % Chitosan, 78% 4-t-Butylstyrene, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2wt % infrared dye in ethanol. After drying at 60° C. for 2 minutes, theplate was imaged using infrared laser exposure of 500 mJ/cm² at 15Watts. The imaged plate was mounted onto a press (Multi), dampened withfountain solution for 30 seconds before the ink was applied to theplate. 10,000 impressions were printed on uncoated paper. Duringprinting, the surface on background remains unchanged.

Example 22

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PCIS/AA copolymer (13 wt % Chitosan, 78% 4-Chloro styrene,9% Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2 wt %infrared dye in ethanol. After drying at 60° C. for 2 minutes, the platewas imaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Multi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 4000impressions were printed on uncoated paper. During printing, the surfaceon background remains unchanged.

Example 23

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/Pα MS/AA copolymer (13 wt % Chitosan, 78% α-methylstyrene, 9% Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2wt % infrared dye in ethanol. After drying at 60° C. for 2 minutes, theplate was imaged using infrared laser exposure of 500 mJ/cm² at 15Watts. The imaged plate was mounted onto a press (Multi), dampened withfountain solution for 30 seconds before the ink was applied to theplate. 4000 impressions were printed on uncoated paper. During printing,the surface on background remains unchanged.

Example 24

A plate was produced by coating the following formulation on to agrained, anodized aluminum plate to give a dry coating weight of 1 g/m²:30 g Chitosan/PMS/AA copolymer (13 wt % Chitosan, 78% 4-methyl styrene,9A Acrylic acid) aqueous dispersion with 10% solid and 9 g of 2 wt %infrared dye in ethanol. After drying at 60° C. for 2 minutes, the platewas imaged using infrared laser exposure of 500 mJ/cm² at 15 Watts. Theimaged plate was mounted onto a press (Multi), dampened with fountainsolution for 30 seconds before the ink was applied to the plate. 1000impressions were printed on uncoated paper. During printing, the surfaceon background remains unchanged.

Example 25

To a 10 L glass reactor equipped with thermometer, mechanical stirring,nitrogen inlet and heating bath, set to 60° C., containing a stirringsolution under nitrogen of 120 g chitosan, 8.52 g of potassiumpersulfate and 8.53 g of sodium metabisulfite in 159 g of acetic acidand 7910 g of water, was added 712 g of styrene and 80 g of acrylicacid. After 6 hours, stirring was stopped and the reactor contents werefiltered to give an opaque white liquid, 3 g of which was mixed with 1 gof 1% infrared dye in ethanol and 1 g of 0.2% wetting agent in water.When coated onto an aluminum substrate, dried, imaged with 830 nm laserradiation with an exposure of 300 mJ/cm² the resulting plate printed toover 5,000 pages without loss of coating in either exposed or unexposedareas.

Example 26

To a 10 L glass reactor equipped with thermometer, mechanical stirring,nitrogen inlet and heating bath, set to 60° C., containing a stirringsolution under nitrogen of 120 g chitosan, 8.52 g of potassiumpersulfate and 8.53 g of sodium metabisulfite in 159 g of acetic acidand 7910 g of water, was added 633 g of styrene, then 158 g of acrylicacid. After 6 hours, stirring was stopped and the reactor contents werefiltered to give an opaque white liquid, 3 g of which was mixed with 1 gof 1% infrared dye in ethanol and 1 g of 0.2% wetting agent in water.When coated onto an aluminum substrate, dried, imaged with 830 nm laserradiation with an exposure of 300 mJ/cm², the resulting plate printed toover 5,000 pages without loss of coating in either exposed or unexposedareas.

Example 27

In a 2 L glass vessel equipped with mechanical stirring and nitrogenatmosphere was prepared a mixture of 791.99 g deionized water, 19.27 gacetic acid, 12.10 g chitosan and 0.0723 g iron gluconate having aviscosity of 32.6 cps at 25° C.; to this was added 57.47 g methylmethacrylate, 6.39 g acrylic acid, 0.229 g Triton X-405 and 80.24 g moredeionized water, then, after stirring at 1200 rpm and 60° C. for 15minutes, a solution of 0.0980 g of ammonium sulfite and 1.080 g of 50%aqueous glyoxylic acid in 12.36 g of deionized water with rinsing by 1.0g of deionized water, then after 10 minutes still stirring at 1200 rpm,1.188 g of 55% pinane hydroperoxide in pinane, then after a further 10minutes at 800 rpm, a further 0.584 g of 55% pinane hydroperoxide inpinane, then after a further 5 minutes at 800 rpm then 10 minutes at 400rpm, a further solution of 0.979 g of ammonium sulfite and 1.079 g of50% aqueous glyoxylic acid in 12.34 g of deionized water with rinsing by1.0 g of deionized water. During this time the pot temperature had risenby 7° C.; after a further 90 minutes at 400 rpm, the hot opaque whiteliquid was passed through successive filters having nominal ratings of100, 10 then 1 microns. The resulting filtrate was a latex containingparticles having d(50) diameter of 0.138 microns by light-scattering,for 7.94% nonvolatile solids (expected 8.00% from the monomers).

38.7 g of a latex made according to the above recipe was mixed with 7.9g of 2% acetic acid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IRdye and 0.84% of a wetting agent and 0.025% glyoxal when coated on agrained and anodized aluminum substrate, dried to give a dry coatweightof ca. 1.8 gsm, imaged using infrared exposure of 275 mJ/cm² at 15Watts. The imaged plate was mounted onto a press, dampened with fountainsolution for 30 seconds before the ink was applied to the plate. Over25,000 impressions without loss of coating in either exposed orunexposed areas were printed. During printing, the surface on thebackground remains unchanged.

Example 28

In a 10 L glass vessel equipped with mechanical stirring and nitrogenatmosphere was prepared a mixture of 7158.41 g deionized water, 172.95 gacetic acid, 108.76 g chitosan and 1.160 g iron gluconate having aviscosity of 18.5 cps at 25° C.; to this was added 518.88 g methylmethacrylate, 57.43 g acrylic acid, 2.03 g Triton X-405 and 698.28 gmore deionized water, then, after stirring at 340 rpm and 80° C. for 10minutes, a solution of 8.81 g of ammonium sulfite and 9.72 g of 50%aqueous glyoxylic acid in 111.08 g of deionized water with rinsing by5.0 g of deionized water, then after 10 minutes still stirring at 340rpm, 10.546 g of 55% pinane hydroperoxide in pinane, then after afurther 10 minutes at 340 rpm, a further 5.293 g of 55% pinanehydroperoxide in pinane, then after a further 15 minutes at 340 rpm, afurther solution of 8.80 g of ammonium sulfite and 9.71 g of 50% aqueousglyoxylic acid in 110.95 g of deionized water with rinsing by 5.0 g ofdeionized water. During this time the pot temperature had risen by 9°C.; after a further 5 minutes at 340 rpm, then 85 minutes at 180 rpm,the hot opaque white liquid was passed through successive filters havingnominal ratings of 100, 10 then 1 microns. The resulting filtrate was alatex containing particles having d(50) diameter of 0.133 microns bylight-scattering, for 7.88% nonvolatile solids (expected 8.02% from themonomers).

34.8 g of a latex of this recipe was mixed with 11.8 g of 2% acetic acidand 3.4 g of 1-methoxy-2-propanol containing 2.8% IR dye and 0.84% of awetting agent and 0.025% glyoxal when coated on a grained and anodizedaluminum substrate, dried to give a dry coatweight of ca. 1.8 gsm,imaged using infrared exposure of 275 mJ/cm2 at 15 Watts. The imagedplate was mounted onto a press, dampened with fountain solution for 30seconds before the ink was applied to the plate. Over 25,000 impressionswithout loss of coating in either exposed or unexposed areas wereprinted. During printing, the surface on the background remainsunchanged.

Example 29

34.8 g of the latex of example 28 was mixed with 11.8 g of 2% aceticacid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR dye and 0.84%of a wetting agent and 0.025% glyoxal when coated on a grained andanodized aluminum substrate, dried to give a dry coatweight of ca. 1.8gsm, a second layer was then applied by spraying from a solutioncomprising 0.2 g of 25% gum arabic solution and 0.005 g wetting agentand 9.5 g DI water, dried to give a dry coatweight of ca. 0.03 gsm,imaged using infrared exposure of 275 mJ/cm2 at 15 Watts. The imagedplate was mounted onto a press, dampened with fountain solution for 30seconds before the ink was applied to the plate. Over 25,000 impressionswithout loss of coating in either exposed or unexposed areas wereprinted. During printing, the surface on the background remainsunchanged. The benefit of a topcoat was observed when the plate with andwithout a topcoat was press tested after 6 weeks storage under ambientconditions. The press results are summarized in Table 1 below.

TABLE 1 Number of printed sheets required to give a tone free backgroundin the printed sheet After 1 week After 6 weeks example 28 ≦10 700example 29 ≦10 ≦10

Example 30

34.8 g of the latex of example 28 was mixed with 11.8 g of 2% aceticacid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR dye and 0.84%of a wetting agent and 0.025% glyoxal when coated on a grained andanodized aluminum substrate, dried to give a dry coatweight of ca. 1.8gsm, a second layer was then applied by coating a solution comprising2.5% (by weight) gum arabic solution in DI water, which was then driedto give a dry coatweight of ca. 0.1 gsm. A higher topcoat coatweight wasachieved by coating a 5% (by weight) gum arabic solution, which gave ca.0.1 gsm.

Plates based on example 28 and the present example 30 were then storedat 30 C and 85% relative humidity for 5 days. The purpose of this testis to accelerate the aging of the plate seen at lower temperature andhumidity conditions. These plates were then imaged using infraredexposure of 325 mJ/cm2 at 17.4 Watts. The imaged plate was mounted ontoa press, dampened with fountain solution for 30 seconds before the inkwas applied to the plate. The number of printed sheets required to givea dean background on the printed sheet was noted as well as the tendencytowards plugging of the shadows and the print quality of the plate aresummarized in the Table 2.

TABLE 2 Number of copies Topcoat Aged at 30 C. to obtain a cleanPlugging of Presence of 2% dots at Example coatweight @85% RH backgroundon the the 240 Ipi imaged at number (gsm) 5 days printed sheet shadows325 mJ/cm2 28 None No ≦10 No Complete 28 None Yes >3,000 Yes Complete 30ca. 0.05 Yes <10 No Complete 30 ca. 0.1 Yes <10 No Incomplete

Example 31

34.8 g of the latex of example 28 was mixed with 11.8 g of 2% aceticacid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR dye and 0.84%of a wetting agent and 0.025% glyoxal when coated on a grained andanodized aluminum substrate, dried to give a dry coatweight of ca. 1.8gsm, a second layer was then applied by coating from a solutioncomprising 0.1 μg of polyvinyl alcohol, 0.02 g of chitosan, 0.01 g ofglucose, 0.22 acetic acid and 9.64 g DI water, dried to give a drycoatweight of ca. 0.01 gsm. A higher topcoat coatweight was achieved bycoating a solution comprising 0.22 g of polyvinyl alcohol, 0.049 ofchitosan, 0.02 g of glucose, 0.44 g acetic acid and 9.28 g DI water,which gave a topcoat coat weight of ca. 0.1 gsm.

Plates based on example 28 and present example 31 were then stored at 30C and 85% relative humidity for 5 days. These plates were then imagedusing infrared exposure of 325 mJ/cm2 at 17.4 Watts. The imaged platewas mounted onto a press, dampened with fountain solution for 30 secondsbefore the ink was applied to the plate. The number of printed sheetsrequired to give a clean background on the printed sheet was noted aswell as the tendency towards plugging of the shadows and the printquality of the plate are summarized in the Table 3.

TABLE 3 Number of copies Topcoat Aged at 30 C. to obtain a cleanPlugging Presence of 2% dots at Example coatweight @85% RH background onthe of the 240 Ipi imaged at number (gsm) 5 days printed sheet shadows325 mJ/cm2 28 None No ≦10 No Complete 28 None Yes 400 Yes Complete 31ca. 0.01 Yes <10 No Complete 31 ca. 0.1 Yes <10 No Incomplete

Example 32

34.8 g of the latex of example 28 was mixed with 11.8 g of 2% aceticacid and 3.4 g of 1-methoxy-2-propanol containing 2.8% IR dye and 0.84%of a wetting agent and 0.025% glyoxal when coated on a grained andanodized aluminum substrate, dried to give a dry coatweight of ca. 1.8gsm, a second layer was then applied by coating from a solutioncomprising 0.13 g of polyvinyl alcohol and 0.01 g of glucose and 9.86 gDI water, dried to give a dry coatweight of ca. 0.01 gsm. A highercoatweight was achieved by coating a solution comprising 0.26 g ofpolyvinyl alcohol and 0.02 g of glucose and 9.72 g DI water, dried togive a dry coatweight of ca. 0.1 gsm

Plates based on examples 28 and present example 32 were then stored at30 C and 85% relative humidity for 5 days. These plates were then imagedusing infrared exposure of 325 mJ/cm2 at 17.4 Watts. The imaged platewas mounted onto a press, dampened with fountain solution for 30 secondsbefore the ink was applied to the plate. The number of printed sheetsrequired to give a clean background on the printed sheet was noted aswell as the tendency towards plugging of the shadows and the printquality of the plate are summarized in the Table 4.

TABLE 4 Number of copies Topcoat Aged at 30 C. to obtain a cleanPlugging Presence of 2% dots at Example coatweight @85% RH background onthe of the 240 Ipi imaged at number (gsm) 5 days printed sheet shadows325 mJ/cm2 28 None No ≦10 No Complete 28 None Yes 50 Yes Complete 32 ca.0.01 Yes <10 No Complete 32 ca. 0.1 Yes <10 No Incomplete

Example 33

34.8 g of the latex of example 28 was mixed with 11.8 g of 2% aceticacid and 3.4 a of 1-methoxy-2-propanol containing 2.8% IR dye and 0.84%of a wetting agent and 0.025% glyoxal when coated on a grained andanodized aluminum substrate, dried to give a dry coatweight of Ca. 1.8gsm, a second layer was then applied by coating from a solutioncomprising 0.11 g of polyvinyl alcohol and 0.149 of gum arabic and 9.75g DI water, dried to give a dry coatweight of ca. 0.01 gsm. A highertopcoat coat weight was achieved by coating a solution comprising 0.22 gof polyvinyl alcohol and 0.28 g of gum arabic and 9.5 g DI water, driedto give a dry coatweight of ca. 0.1 gsm

Plates based on examples 30, 31, 32 and present example 33 were thenstored at 30 C and 85% relative humidity for 5 days. These plates werethen imaged using infrared exposure of 325 mJ/cm2 at 17.4 Watts. Theimaged plate was mounted onto a press, dampened with fountain solutionfor 30 seconds before the ink was applied to the plate. The run lengthperformance is summarized in Table 5.

TABLE 5 Number of copies Topcoat Aged at 30 C. to obtain a cleanPlugging Example coatweight @85% RH background on the of the number(gsm) 5 days printed sheet shadows Run length 28 None No ≦10 No >30,00030 ca. 0.1 Yes <10 No >30,000 31 ca. 0.01 Yes <10 No >30,000 32 ca. 0.01Yes <10 No >30,000 33 ca. 0.01 Yes <10 No >30,000

There have thus been outlined the important features of the invention inorder that it may be better understood, and in order that the presentcontribution to the art may be better appreciated. Those skilled in theart will appreciate that the conception on which this disclosure isbased may readily be utilized as a basis for the design of othercompositions, elements and methods for carrying out the several purposesof the invention. It is most important, therefore, that this disclosurebe regarded as including such equivalent compositions, elements andmethods as do not depart from the spirit and scope of the invention.

1. A processless radiation-imageable lithographic printing precursorcomprising a substrate, a dried and aqueous-ineluable coating of aradiation-sensitive medium on the substrate and an aqueous eluablehydrophilic overcoat over the coating of a radiation-sensitive medium,the radiation-sensitive medium comprising: a. a substance capable ofconverting radiation into heat; and b. hydrophilic polymer particlescomprising: i. at least one thermally softenable hydrophobic polymer,ii. at least one hydrophilic polymer and iii. at least one bondingcompound capable of chemically bonding to the hydrophobic polymer and tothe hydrophilic polymer.
 2. The precursor of claim 1, wherein theaqueous eluable hydrophilic overcoat comprises a water-soluble organicpolymer.
 3. The precursor of claim 2, wherein the water-soluble organicpolymer is at least one of polyvinylalcohol, polyvinylacetate,polyacrylic acid, poly(meth)acrylic acid, an alkali metal salt ofpoly(meth)acrylic acid, an amine salt of poly(meth)acrylic acid, poly2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, polyvinyl methylether, polyvinyl methyl ether/maleic anhydride copolymer,polyvinylpyrolidone, poly-2-acrylamide-2-methylpropane sulfonic acid, analkali metal salt of poly-2-acrylamide-2-methylpropane sulfonic acid, anamine salt of poly-2-acrylamide-2-methylpropane sulfonic acid, alginicacid, a salt of alginic acid, protan jelly, carageenin, tragacanth,laminarin sulfate, starch, animal glues, vegetable mucilages, gumarabic, cellulose, a modification product of cellulose and apolysaccharide.
 4. The precursor of claim 3, wherein the overcoatfurther comprises at least one of a light-to-heat converting agent, awater-soluble dye, a colorant and a surfactant.
 5. The precursor ofclaim 2, wherein the coating is capable of becoming hydrophobic underthe action of heat.
 6. The precursor of claim 5, wherein the substancecapable of converting radiation into heat is hydrophobic.
 7. Theprecursor of claim 5, wherein the radiation is infrared radiation. 8.The precursor of claim 7, wherein the infrared radiation has wavelengthbetween 700 nm and 1200 nm n.
 9. The precursor of claim 5, wherein thehydrophilic polymer has a primary amine group.
 10. The precursor ofclaim 5, wherein the at least one hydrophilic polymer is at least one ofa saccharide, a chitosan polymer, a polyethyleneimine polymer, apolyamine polymer, a polyvinylamine polymer, a polyallylamine polymer, apolydiallylamine polymer, an amino(meth)acrylate polymer, a polyamidepolymer, a polyamide-epichlorohydrin polymer, apolyamine-epichlorohydrin polymer, a polyamidepolyamine-epichlorohydrinpolymer, a dicyandiamide-polycondensation product polymer and acopolymer thereof.
 11. A method for making a negative-workinglithographic printing master, the method consisting essentially of, inthe order stated, imagewise irradiating the processlessradiation-imageable lithographic printing precursor of claim 10 withimaging radiation and treating the precursor with an aqueous medium. 12.A processless radiation-imageable lithographic printing precursorcomprising a substrate, a dried and aqueous-ineluable coating of aradiation-sensitive medium on the substrate and an aqueous eluablehydrophilic overcoat over the coating of a radiation-sensitive medium,the radiation-sensitive medium comprising: a. a substance capable ofconverting radiation into heat; and b. a hydrophilic polymer; and c atleast one copolymer of a hydrophobic monomer and a bonding monomer, thebonding monomer being capable of chemically bonding to the hydrophilicpolymer and to the hydrophobic monomer.
 13. The precursor of claim 12,wherein the aqueous eluable hydrophilic overcoat comprises awater-soluble organic polymer.
 14. The precursor of claim 13, whereinthe water-soluble organic polymer is at least one of polyvinylalcohol,polyvinylacetate, polyacrylic acid, poly(meth)acrylic acid, an alkalimetal salt of poly(meth)acrylic acid, an amine salt of poly(meth)acrylicacid, poly 2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, polyvinylmethyl ether, polyvinyl methyl ether/maleic anhydride copolymer,polyvinylpyrollidone, poly-2-acrylamide-2-methylpropane sulfonic acid,an alkali metal salt of poly-2-acrylamide-2-methylpropane sulfonic acid,an amine salt of poly-2-acrylamide-2-methylpropane sulfonic acid,alginic acid, a salt of alginic acid, protan jelly, carageenin,tragacanth, laminarin sulfate, starch, animal glues, vegetablemucilages, gum arabic, cellulose, a modification product of celluloseand a polysaccharide.
 15. The precursor of claim 12, wherein theovercoat further comprises at least one of a light-to-heat convertingagent, a water-soluble dye, a colorant and a surfactant.
 16. Theprecursor of claim 13, wherein the coating is capable of becominghydrophobic under the action of heat.
 17. The precursor of claim 16,wherein the substance capable of converting radiation into heat ishydrophobic.
 18. The precursor of claim 17, wherein the radiation isinfrared radiation.
 19. The precursor of claim 18, wherein the infraredradiation has wavelength between 700 nm and 1200 nm.
 20. The precursorof claim 16, wherein the hydrophilic polymer has a primary amine group.21. The precursor of claim 16, wherein the at least one hydrophilicpolymer is at least one of a saccharide, a chitosan polymer, apolyethyleneimine polymer, a polyamine polymer, a polyvinylaminepolymer, a polyallylamine polymer, a polydiallylamine polymer, anamino(meth)acrylate polymer, a polyamide polymer, apolyamide-epichlorohydrin polymer, a polyamine-epichlorohydrin polymer,a polyamidepolyamine-epichlorohydrin polymer, adicyandiamide-polycondensation product polymer and a copolymer thereof.22. A method for making a negative-working lithographic printing master,the method consisting essentially of, in the order stated, imagewiseirradiating the processless radiation-imageable lithographic printingprecursor of claim 21 with imaging radiation and treating the precursorwith an aqueous medium. 23.-44. (canceled)
 45. A processlessradiation-imageable lithographic printing precursor comprising asubstrate, a dried and aqueous-ineluable hydrophilic coating of aradiation-sensitive medium on the substrate and an aqueous eluablehydrophilic overcoat over the coating of a radiation-sensitive medium,the radiation-sensitive medium comprising hydrophilic polymer particles,the particles comprising chitosan and at least one thermally softenablehydrophobic polymer, the coating capable of becoming hydrophobic underthe action of heat.
 46. The precursor of claim 45, wherein the aqueouseluable hydrophilic overcoat comprises a water-soluble organic polymer.47. The precursor of claim 46, wherein the water-soluble organic polymeris at least one of polyvinylalcohol, polyvinylacetate, polyacrylic acid,poly(meth)acrylic acid, an alkali metal salt of poly(meth)acrylic acid,an amine salt of poly(meth)acrylic acid, poly2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, polyvinyl methylether, polyvinyl methyl ether/maleic anhydride copolymer,polyvinylpyrollidone, poly-2-acrylamide-2-methylpropane sulfonic acid,an alkali metal salt of poly-2-acrylamide-2-methylpropane sulfonic acid,an amine salt of poly-2-acrylamide-2-methylpropane sulfonic acid,alginic acid, a salt of alginic acid, protan jelly, carageenin,tragacanth, laminarin sulfate, starch, animal glues, vegetablemucilages, gum arabic, cellulose, a modification product of celluloseand a polysaccharide.
 48. The precursor of claim 47, wherein theovercoat further comprises at least one of a light-to-heat convertingagent, a water-soluble dye, a colorant and a surfactant.
 49. A methodfor making a negative-working lithographic printing master, the methodcomprising the steps of: a. providing a precursor comprising a dried andaqueous-ineluable coating of a radiation-sensitive medium on a substrateand an aqueous eluable hydrophilic overcoat over the coating of aradiation-sensitive medium, the radiation-sensitive medium comprisinghydrophilic polymer particles, the particles comprising chitosan and atleast one thermally softenable hydrophobic polymer, the coating beinghydrophilic and capable of becoming hydrophobic under the action ofheat, b. imagewise irradiating the precursor with infrared imagingradiation of wavelength between 700 nm and 1200 nm and c treating theprecursor with an aqueous medium.
 50. The method of claim 49, whereinthe aqueous eluable hydrophilic overcoat comprises a water-solubleorganic polymer.
 51. The method of claim 50, wherein the water-solubleorganic polymer is at least one of polyvinylalcohol, polyvinylacetate,polyacrylic acid, poly(meth)acrylic acid, an alkali metal salt ofpoly(meth)acrylic acid, an amine salt of poly(meth)acrylic acid, poly2-hydroxyethyl(meth)acrylate, poly(meth)acrylamide, polyvinyl methylether, polyvinyl methyl ether/maleic anhydride copolymer,polyvinylpyrollidone, poly-2-acrylamide-2-methylpropane sulfonic acid,an alkali metal salt of poly-2-acrylamide-2-methylpropane sulfonic acid,an amine salt of poly-2-acrylamide-2-methylpropane sulfonic acid,alginic acid, a salt of alginic acid, protan jelly, carageenin,tragacanth, laminarin sulfate, starch, animal glues, vegetablemucilages, gum arabic, cellulose, a modification product of celluloseand a polysaccharide.
 52. The method of claim 51, wherein the overcoatfurther comprises at least one of a light-to-heat converting agent, awater-soluble dye, a colorant and a surfactant.